Faciès, stratigraphic architecture and sedimentary dynamics in glacio-isostatically forced-regression : the pro- to paraglacial response of the deltaic complexes of the North Shore of the St. Lawrence Estuary and Gulf (Québec, Canada)

• Main Author: Dietrich, Pierre
• Other Authors: Institut de physique du globe de Strasbourg (IPGS), Université de Strasbourg (UNISTRA)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Université de Strasbourg, Jean-François Ghienne
• Format: Doctoral or Postdoctoral Thesis
• Language: French
• Published: HAL CCSD 2015
• Subjects: Deglaciation; Delta; Outwash fan; Raised beaches; Glacio-isostatic rebound; Falling-Stage System Tract; St. Lawrence North Shore; Laurentide Ice Sheet; Inlandsis Laurentidien; Côte Nord du St. Laurent; Cortège de régression forcée; Rebond glacio-isostatique; Plages soulevées; Épandage juxtaglaciaire; Déglaciation; [SDU.STU.GL]Sciences of the Universe [physics]/Earth Sciences/Glaciology; Canada; Ice Sheet; Inlandsis
• Online Access: https://tel.archives-ouvertes.fr/tel-01291667; https://tel.archives-ouvertes.fr/tel-01291667/document; https://tel.archives-ouvertes.fr/tel-01291667/file/Dietrich_Pierre_2015_ED413.pdf

The North Shore of the St. Lawrence Estuary and Gulf is characterized by the presence of deltaic complexes that were emplaced under falling Relative Sea Level (RSL) forced by the glacio-isostatic rebound, immediately after the retreat of the Laurentide Ice Sheet (LIS) margin. The study of three deltaic complexes reveals that a common morphostratigraphic evolution forced by the retreat of the LIS prevailed for the edification of these structures, reflecting the retreat of the LIS margin. The emplacement of subaqueous outwash fans beyond the retreating or stillstanding glaciomarine margin constitutes the first stage of this evolution. As tied to the ice-margin position, these fans are characterized in places by a backstepping stacking pattern, in spite of the forced regressive setting. From the emergence of a continental ice front, the proglacial deltaic system develops and forms lobes staged accordingly to the RSL fall. These deltaic systems actively prograde at that time because they are fed in glaciogenics by the retreating LIS margin through braided meltwater streams. In spite of the RSL fall reaching several centimeters per years, no fluvial entrenchment occurs mainly owing to the significant amount of sediment supply. Later, when the LIS margin retreats from the drainage basins of feeding rivers, fluvial systems experience a drastic drop in sediment supply that forced the interruption of the deltaic progradation and the onset of paraglacial reworking. The paraglacial reworking consists in the entrenchment of a meandering fluvial system within former deltaic deposits and shows the prevalence of shallow-marine processes (waves, tides) at the delta rim (raised beaches, marine terraces). This study reveals that the bulk of the deltaic volume (c.a. 10-20 km3) for each complex was emplaced in only a few thousands of years following the LIS margin retreat when the latter was still located in the drainage basin. The paraglacial reworking had a minor influence on the deltaic accretion. A forward stratigraphic model ...